Although the promoters and terminators of several rRNA operons have been sequenced, the regions involved in specific control functions regulating rRNA transcription have not yet been identified. To facilitate that identification, I plan to construct mini-rrn operons containing either the rrnX or rrnD promoter fused to unique marker genes which are followed by either the rrnC or rrnG(E) terminator. These mini-operons will provide sequenced starting material for constructing site specific mutational alterations at predicted control regions. The mini-operons or their derivatives can then be transformed into appropriate E. coli mutants to analyze their expression in vivo. The in vivo studies combined with in vitro transcriptional analysis of the DNA should allow definition of the controlling sequences necessary for rRNA expression. They may also be able to pinpoint the site of action of the E. coli mutants.